Coordinated fuel feed and exhaust jet area control for gas turbine engines



Oct. ll, 1960 B. s. HEGG ET AL 2,955,416

COORDINATED FUEL FEED AND EXHAUST JET AREA CONTROL Fon GAS TURBINE ENGINES Original Filed May l5. 1952 4 Sheets-Sheet 1 47m/mfr B. S. FUEL Oct. 11, 1960 HEGG EI'AL 2,955,416 COORDINATED FEED AND EXHAUST JET AREA CONTROL FOR GAS TURBINE ENGINES 1952 4 Sheets-Sheet 2 Original Filed May l5.

B. S. HEGG ET AL COORDINA'IED FUEL 2,955,416 FEED AND EXHAUST JET AREA CONTROL FOR GAS TURBINE ENGINES 1952 4 Sheets-Sheet 3 Oct. 11, 1966 Original Filed May 15,

INVENTOR. 35. #66

Oct l-l 1960 a. s. HEGG ETAL 2 955 416 cooEnrN-ETED FUEL FEED AND EXHAUST JET AREA CONTROL FOR GAS TURBNE ENGINES Original Filed May 15, 1952 4 Sheets-Sheet 4 VOLTAGE EFEPENCE 1 REGUUI'E 440 CYCLE TUBE POWER IN PUT SPE E D SUPPLY ARMING 5W|TCH RELAY B+@ To AMPUFIERS NO @I ZEP-RI PHAsE REFERENCE AMPLIFIE AMPMFIE AMPLIFIE siNsvTlvE BRIDGE & l 81 URCUIT MIXER MIXER & TAIL PIPE Y mDuLATo Mm AM THERMO' L P COYR: A E 5l COUPLE TEMP. RATE 5mm.

i-TE .E

2,955,415 Patented Oct. 11, 1960 iii-1 COORDINATED FUEL FEED AND EXHAUST .FET AREA 'CONTROL FOR GAS TURBINE ENGINES illy S. Hegg and Norman K. Peters, South Bend, Ind., assignors to The Bendix ICorporation, a corporation of Delaware continuation of application ser. No. 281,926, May 1s, 1952. This application Oct. '6, 1958,`Ser. No. 765,675

4 Claims. (Cl. 60-35.`6)

This application is `a continuation of our application Serial No. 287,926, tiled May l5, 1952, nowV abandoned, which is a continuation-impart of our application Serial No. 212,566, filed February 24, 1951, now abandoned. Both applications relate to controls for gas turbine engines, and particularly to controls of a type wherein the rate of fuel feed and the area of the exhaust jet or nozzle are coordinated over la predetermined portion of the power throttle range subject to the action of an override device responsive to temperature, speed or other operating condition or parameter. An example of such a control is illustrated in the copending application of Frank C. Mock, Serial No. 156,980, filed April 20, 1950, now abandoned (common assignee).

An object of the instant invention is to provide a control mechanism of the type specified which may be responsive to throttle movement through the afterburner range for establishing a predetermined exhaust area opening and responsive to electronic engine temperature sensing means for modifying the exhaust area opening.

' hydraulic actuator;

readily adapted to certain desired conditions of engine operation. Thus, in the example illustrated, the improved control will automatically maintain the exhaust jet or nozzle at maximum Varea at power lever4 positions and engine speeds below a predetermined value; and at power lever positions and engine speeds above such value and at tailpipe temperatures below a predetermined value, the exhaust jet area will vary in response to adjustment of said lever; and should the tailpipe temperature rise beyond the set or predetermined temperature with the exhaust jet or nozzle at any area less than maximum, the power levercontrol will be overridden and the exhaust jet area will be automatically increased until the tailpipe temperature drops to a safe value. Should the pilot attempt to reduce the area of the exhaust jet to alvalue which will produce unsafe tailpipe temperatures, the power lever control will again be overridden and jet nozzle area will vary as a function of a tailpipe temperature only.

Another object is to coordinate the action of a hydraulic and an electronic control for regulating the exhaust jet area of a turbojet engine.

A further object is to improve the control mechanism disclosed in the application of Frank C. Mock above noted.

Another object is to coordinate the action of a hydraulic mechanism with an engine temperature sensing electronic control for regulating the exhaust areaV of a gas turbine engine.

A still further object resides in the provision of mechanism operatively connected to an engine throttle and to an exhaust area control device for selecting an effective exhaust area corresponding to a given throttle position regardless of whether the throttle settingis in the power range or afterburner range. y

A yet further object is to provide an exhaust area control mechanism for a gas turbine engine operatively connected to an engine throttle, which coordinates fuel feed with exhaust opening, and to an engine temperature sensing apparatus which automatically modiles the exhaust opening.

Another important object is to provide a mechanism It is one of the aims of this invention to coordinate control of the engine exhaust area, the main fuel control and afterburner control with throttle position subject, however, to modification when engine temperature is beyond a predetermined value.

The foregoing and other objects and advantages will become apparent in view of the following description taken in conjunction with the drawings, wherein:

Figure l is a View, principally in elevation, of a turbojet engine having operatively associated therewith a control embodying the features of the instant invention;

Figure 2 is a sectional schematic view of the hydraulic actuator for the jet nozzle area varying valve or bullet;

Figure 2a illustrates a modified cam construction;

Figure 3 is a wiring diagram of the electronic temperature responsive control and amplifier control for the Figure 4 is a block diagram of the circuitry of Figure 3; Y

Figure 5 is a graph illustrating the operation of the bridge circuit of Figure 3; and Y Figure 6 is a curve chart illustrating the operation of the control.

Referring to Figure 1, a turbojet engine is shown more or less diagrammatically at 10; it includes a burner section 1,1, and air adapter or header section 12 detachably connected to the front end of the burner section and adapted to direct air under pressure from an axial flow compressor notshown to the burners, where the air mixes with the fuel discharged from the burner nozzles to promote combustion, the expanded air and products of combustion being discharged through a turbine section 13, tailpipe 14, and a reaction jetor exhaust nozzle 15. The arc of the exhaust jet is variableby suitable means such as a bullet valve or cone `16, mounted to move inwardly and outwardlyrof the exhaust jet on suitable guides, not shown.

Fuel is supplied to a main fuel `manifold 17 of the main burner system by a suitable fuel control .device generally indicated at 17, which is preferably of the type disclosed in the copending application ofFrank C. Mock aforementioned, and wherein the engine speed as selected by the pilot is automatically maintained by an engine driven all-speed governor at all altitudes irrespective of changes in the pressure and/or temperature of the air flowing to the engine. A pilot actuated power control lever is indicated at 18; it is secured-on a shaft 19 and the latter is operatively connected to the governor valve of -therfuel control unit 17 through a gear 20 and rack 21. Also secured on shaft 19 is a gear 22 in mesh with a rack 23, which projects into the hydraulic actuator for a purpose to be described.

The engine of Figure 1 is further equipped with an afterburner fuel system ofthe type shown in the copending application of Frank'C. Mock, et al., Serial No. 89,054, lled April 22, 1949, now Patent No. 2,774,215, assigned to a common assignee,'and comprises an afterburner fuel control device 17 and an afterburner manifold 17". The pilot actuated power control lever or throttle r18 is also connected to the afterburner control device 17 through a mutilated gear sector 20 and linkage 21', the latter including a rack portion 21", which is arranged to be engaged by the mutilated gear sector 20 only after the throttle has been moved through 90, as best shown in dotted lines, Figure. That is, it is not until after the lever 18 has been moved through the power range, 52 to 90, that the afterburner system becomes effective as an additional fuel supply, thus supplementing the main fuel supply to the engine. The addition of fuel at the proper time beyond that supplied by the main fuel control augments the engine thrust. Therefore, the range between 93 and 110 of the pilot control member is known as the thrust augmentation range. The 3 allowed between 90 and 93 permits some throttle movement at the end of the power' range, before going into the afterburner range. Movement of the throttle between 90 and 93 has no further effect on the power range.

The bullet valve or cone 16 is repositioned or reset by means of a hydraulic servo motor generally indicated at 25 and having mounted therein a servo piston 25', note Figure 2. High pressure oil or hydraulic uid is conducted to the cylinder 25 on vopposite sides of piston 25 by way of high pressure oil lines 26 and 27, which lead from a servo valve 28 located in the housing 249 of the `actuator mechanism. The servo valve 28 (Figure 2) comprises a suitable cylinder having slidably mounted therein a pair of valve pistons 30 and 31, which control the exhaust `areas to the annular lands or recesses 32 and 33, from which ports 34 and 35 lead to the oil lines 27 and 26. The valve pistons 30 and 31 are carried by a slide rod 36, which constitutes a cam follower and has a cam surface 36' at its `free end engaging the Vactive surface of a motor driven cam 37, splined for limited longitudinal sliding movement on a shaft 38, adapted to be driven by a motor 39 through a gear reduction unit 40, the said motor being a two-phase servo motor controlled in a manner to be described. When the power is off, a spring 41 returns or rotates the motor or armature shaft 38 back to a position where the one end v42 of a stop arm 42 carried by the shaft engages an under-temperature stop 43. ln `actual practice, the spring 41 is located on the gear reduction unit 40 and the latter drives cam 37 through an additional reduction unit, but for purpose of illustration, the said spring is shown exteriorly of the reduction unit and surrounding the shaft 3S. An overtemperature stop 44 is also adapted to be engaged by the end 42' of arm 42 under certain conditions of operation to be described.

Hydraulic fluid such as oil under pressure is conducted to the servo valve 28 through oil line or conduit 45 and port 45', and is exhausted or drained therefrom by way of exhaust ports 46 and 46" and oil line or conduit 46. A spring47 normally urges the cam end 36 of the piston or follower rod 36 'against the active surface of the cam 37.

The cam 37 is actuated axially on the splined portion of the 'shaft 38 by means of a link bar 48, which is pivotally connected at 49 to said cam, the bar 48 having a pivot and slot connection 49 at one end to a slidable rod or cam follower 50 and at its opposite end being pivoted to a similar rod or follower 51.

A throttle cam 52 is secured on a shaft 53, which is rotated by means of a pinion 54, adapted to engage a rack bar 55, the latter having teeth in mesh with those of a segmental gear 56, secured on a shaft 57. Also secured on the latter shaft is a -pinion 57' having teeth in mesh with those of the rack bar 23 and which is actuated in response to adjustment of the pilots control lever 18, Figure 1. The cam 52, when rotated, actulates the follower rod 51.

The follower rod 50 is actuated by means of a followup cam 58, which is secured on a shaft 59. Also secured on the same shaft is a pinion 60, the teeth of which are in mesh with thoseof a worm 61, secured on the one end of a follow-up shaft 62, the latter extending back to the tailpipe section and at its opposite end being provided with a bevelgear 63, note Figure 1, in mesh with a similar gear `64, secured on the adjacent end of a shaft 65. Shaft -65 Aprojects through -and has bearing in the wall of the tailpipe and at its inner end `has secured thereon a pinion 66, the teeth of which are 4 in mesh with those of a rack gear 67, connected to the bullet valve 116, note Figure 2.

Preferably, the contour of cam 52 is such that it is ineffective to move the servo valve follower rod 51 through the idle range of adjustment, 0 to 52, of the pilots control lever 18. Beyond that range, or throughout the power range, 52 to 90, the cam 52 acts to reset cam 37 longitudinally on the shaft 3S. Rotation of the lever 18 from 93 to 110 is ineffective to move the follower rod 51 since the face 52 o-f the cam 52 on which the follower S1 rides is of constant radius in this range. Figure 2a illustrates a modified cam construction wherein cam 52 functions in the same manner as cam 52 between 0 to 90 throttle movement, but effects a change in exhaust area opening from 93 to 110 throttle rotation. The cam 52 is contoured so that when the throttle is moved into the afterburner range, that is, beyond 93 rotation, the follower rod 51 moves to the left, Figure 2, along the decreasing radius 52" of the cam 52, thus moving the follower 36 to the left to thereby connect the servo motor 25 to the hydraulic source for moving the cone 16 upwardly to increase the exhaust area opening. Afterburner control and exhaust area opening are coordinated with throttle position in the 93 to 110 range, as best shown in Figure 2a.

It will be noted that the effective position of the fcllower rod 36 is also governed by the angular position of cam 37, which is a function of engine or turbine temperature and is capable of overriding the power lever or throttle control.

To preclude the introduction of afterburner fuel into the engine before it is capable of handling fuel in excess of the main supply, a solenoid valve 19 is interposed in the afterburner system between the afterburner control device 17" and the afterburner manifold 17. Energization of the solenoid valve is controlled by an engine `governor operated switch 19". After a predetermined engine speed has been attained, which speed may approach maximum engine speed, the solenoid valve 19 is opened, thus connecting the manifold 17"' to the afterburner control device.

The follow-up cam 58 which is connected to the coneshaped valve 16 through interconnecting linkage, as shown, is contoured so that -rotation of the cam due to movement of the cone will result in a substantially linear relationship between thrust vs. throttle angle.

The motor 39 is controlled electronically as a function of engine temperature subject to modification as a function of engine speed by the circuit shown in Figures 3 'and 4 and which will now be described. ln the wiring vdiagram of Figure 3, capacitors are commonly indicated by C; resistors by R; transformers by T; tubes by V; chokes by L; and choppers and relays by K.

At the right hand side of Figure 3 the motor 39 is shown diagrammatically as having a pair of field windings 70 and 71, one (70) of which constitutes a fixed phase and the other (71) a variable phase winding. The Winding 70 is connected in series with a capacitor C6 to -a tap 72 on the primary of power transformer T5, which 'capacitor introduces a 90 phase shift between the fixed and variable phase windings required for rf'uufimum torque of motor 39. The primary TSA of T5 is supplied with a 400 cycle A.C. input from a suitable source, not shown. The high voltage mid-tapped secondary of T5 is connected to the rectifier tube V10 in a fullwave rectier circuit which changes the 400 cycle per second sine wave into a pulsating `direct current with 800 positive peaks per second, which is smoothed by the low-pass filter circuit including C16, L1, C17, R53, R54 and voltage regulator tubes V8 and V9. The direct cur- ,rent supply, as regulated by tubes V8 and V9, aids in eliminating amplifier gain Variationsand the effect .thereof on control stability. The regulated voltage across V9 provides the required voltage for reference tube V7 and thev dropping resistor R52. Tube V7 is preferably of the cold' cathodel glow discharge type designed for good voltage stability with a negligible temperature coecient.

The reference bridge circuit includes a network of precision wire wound resistors R2'1, R22, R25, R26, R28, and R29, which provide an accurate adjustable reference voltagefor comparison with the voltage generated by the thermocouple 4and also provide for cold junction compensation. Cold junction compensation is provided because the motor control amplifier is required to operate as a function of the hot junction temperature only and not from the thermocouple voltage, which is determined by the `difference between the hot and cold junction temperatures, the latter temperature varying with change in its ambient temperature. We therefore make =a correction for variation in ambient temperatures by utilizing a resistor R25, which is designed so that its re-V sistance varies wit-h changes in temperature and the voltage from 73 to 74 becomes a function of the thermocouple cold junction temperature. As the cold junction temperature increases, the voltage output of the thermo- `couple will decrease for 'a constant hot junction temperature, but the voltage across the temperature cornpensating resistor R25 will increase suiciently to make the voltage `from 73 to '75 independent of the cold junction temperature. This circuit operation is shown graphically in Figure 5. The magnitude of the error voltage developed between 75 and 76 is proportional to the teinperature difference between the amplifier calibration (adjustment of R29) and the thermocouple hot junction temperature. The error voltage polarity is determined -by the relative magnitudes of the two temperatures, viz. 75, is positive with respect to 76 for therrnocouple temperatures greater than the calibration or set temperature and negative for temperatures lower than the calibration temperature. The resistors R23 and R27 have been ladded for safe failure. Thus, should the thermocouple circuit open external to the amplifier or motor control circuit, R23 completes the r'bridge circuit and maintains the equivalent of an under-temperature condition across the bridge. Under normal conditions, R23 has negligible effect on the bridge circuit. The resistor R27 simulates under-temperature operation should the wiper arm of potentiometer R29 open. In case of either failure, the motor control circuit will still arm the actuator control above the speed setting of the speed switch 86 but will not provide a safety override for the throttle control.

The error detector 4and modulator circuits include transformer T1, mechanical modulator or chopper K1, and capacitor C7A. A square wave Voltage is developed across the secondary of the transformer AT, and is proportional to the error signal from the reference bridge. This voltage is in phase or 180 out of phase with the 400 cycle supply, depending upon the error voltage polarity. The error voltage, i.e. the difference between the thermocouple and reference Ivoltages, is modulated by the mechanical chopper K1 at the supply voltageV frequency to permit the use of A.C. amplifiers. At .tailpipe temperatures above or below the calibration tcmperature, current will flow in the primary of T 1 whenever the circuit is completed through armature 77 and contact '78. The resultant output signal of T1 is a close approximation of a square wave with a magnitude proportional to the error voltage between 75 and 76. Overtemperatures cause current flow through the primary of T1 in one direction up and under-temperatures cause flow in the opposite direction down, which results in a signal phase reversal. For example, if it is -assumed that the chopper K1 and transformer T1 are connected to give a signal voltage at the secondary of T1 in phase with the 400 cycle supply voltage for-temperatures ,above the calibration temperature, then the signal voltage will ,be 180 out of phase with the supply voltage for undertemperatures. The capacitor C7A produces a leading current which cancels the mechanical and inductive'lag anemie change; it includes a triode section of amplifier tube V1, amplifier tube V6A and potentiometer 81. The error signal is `amplified by the one triode section of V1 `and its associated resistors R6 and R15. Only the amplied signal lappears across R17 since the direct current is blocked by capacitor C2. The temperature rate signal is added to the error signal at resistor R3, which is common to the `amplifier circuits of both V1 and V6. v R15 and R49 `are large cathode resistors which produce sufcient individual stage degenerative 4feedback to permit tube interchangeability and plus or minus` variation of about ten percent in the heater voltages with negligible amplifier gain variation. Resistor R2 and capacitor C1A comprise a decoupling filter network for reducing the power supply ripple across the V1 and V6 amplifier stages and minimizing regenerative feedback from the output stages. Y

A second stage amplifier and mixer circuit provides for the high amplification of the combined error signaland temperature rate signal with the correction rate signal; it includes the second section of tube V1, amplifier tube V4 and associated resistors including adjustable resistor or potentiometer R34, the latter permitting adjustment of the correction rate signal magnitude. The circuit is The combined error, the temperature rate, and correction rate signals are further amplified by circuitry including .tube V2 and push-pull transformer T2, the latter having its primary capacitively vcoupled to V2 and its secondary connected to the grids of both sections of the driving tube V3 to provide push-pull signals, that is, signal voltages 180 out of phase with one another.

The phase sensitive circuit and magnetic amplifier- T3 comprises the tube V3, and associated capacitors CSA and CSB; its purpose is to convert the low power signal voltage of the signal amplifier circuit to a voltage with adequate power to energize one phase winding, the variable phase 70, of the servo motor 39. The other phase winding 71 issupplied with a fixed voltage through capacitor C6, which shifts the motorvoltage approximately to the supply voltage. The direction of rotation and torque of the two-phase servo motor, which has identical windings, are determined by the voltages applied to the windings and the phase relationship between the two applied voltages. With the voltages to the winding 70 constant, the supply to the other controls the torque and direction of motor rotation. The control voltage is proportional to the error voltage within the saturation limits of ythe amplifier, and the phase relationship to the supply voltage is determined by the polarity of the error voltage. The output tube V3 is biased by the potential divider circuit which includes resistors R11 and R20 connected to the 255 volt regulated D.C. line. The signal output of transformer T2 must tend to change the voltage on one of the grids of V3 in a positive direction at the same instant that the plate voltage is positive to increase conduction in that tube section. If the temperature sensed by the tailpipe thermocouples is exactly equal to the calibration of the unit, there will be no amplifier signal and both sections of V3 will conduct equal currents. Let it be assumed that the secondary TSC of magnetic amplifier T3 is connected to produce positive plate voltages on 4section V3A of tube V3 dur'- ing the period the `grid voltage of the same section is going positive on an overtemperature signal (thermocouple temperatures greater than calibration temperature).

Under these conditions, section VSA will conduct a greater average direct current through winding TSA than VSB conducts through TSD, and with under-temperature fsignals, section VSB will conduct a greater average -direct current through winding TSD than VSA conducts y through TSA. The magnetic amplifier TS is represented schematically by six windings on two cores; its operation may 4be explained on the basis of two transformers having primary windings TSB, TSE, secondary windings TSC, TSF, and control windings TSA, TSD. The two secondary windings are connected series Abucking to the variable phase winding 71 of the servo motor S9. With no direct current or equal currents through the control windings TSA, TSD, the 115 volt supply is divided equally across the primary windings TSB, TSE, the secondary voltages cancel each other and the variable phase winding 71 has no applied voltage. Upon the occurrence of an overtemperature condition, the conduction of a greater average direct current through the control winding TSA than TSD will reduce the primary impedance of TSB below that of TSE. Since the 115 volt supply is divided between the two transformer primaries TSB, TSE in direct proportion to their primary impedances, the secondary voltage developed in TSF will exceed the voltage developed in TSC and the resulting difference is applied to the variable phase winding 71 of motor S9. In a similar manner, an under-temperature condition produces a control voltage, but the latter will be 180 out of phase with the overtemperature voltage. The 180 phase reversal in the voltage applied to the variable phase winding reverses the motor torque.

The temperature rate circuit is designed to produce an A.C. signal with an amplitude proportional to the rate of change of the temperature signal, it includes transformer T4 to which is applied the thermocouple voltage modulated by chopper Kl, first section of amplifier tube V4, cathode follower in the first section of tube V5, rectifier section in the second section of tube V5, two-section filter network including C11, R40, C12A, R41 and C12B, ratesensitive circuit C13, R43 and R48, and mechanical modulator or chopper KS. The A.C. signal is conducted to the first section of V4 from the secondary of T4, where it is amplified and then the amplified signal rectified by the second half of V5. The rectified signal is then filtered by C11, R40, C12A, R41, C12B. The filtered D.C. Voltage across R42 will vary in magnitude in approximately direct proportion to tailpipe temperature. The first section of V5 functions as a cathode follower which provides the required low impedance source for the rectiiier at a signal level nearly equal to that in the high impedance amplifier circuit of V4. The intermediate (rectifying and filtering) step to an A.'C. signal permits stable amplification at a high level without power supply variation effects on the rate signal. The rate-sensitive circuit (C13, R43 and R48) output, which is approximately proportional to the rate of change in the D.C. voltage across R42 is modulated by chopper KS, which shorts out R48 at the line frequency. The resultant A.C. signal is added to the error signal in tube V1 through the mixing action of resistor RS.

A small rate generator 82 is connected to the shaft of the motor S9 and provides a 400 cycle correction rate signal which is fed back into the mixer amplifier tube V1 through capacitor C8, potentiometer RS4, RSS, the second section of tube V4, R8 and R7. T'ne field winding of the generator is supplied with excitation voltage from the 115 volt, 400 cycle input. The generated voltage is directly proportional to the R.P.M. of the actuator motor S9, and its phase relationship to the excitation voltage is a function of the direction of motor rotation. In actual practice, the generator 82 is enclosed within the case of the actuator motor and would not be visible in Figure 2. The correction rate signal feedback into the amplifier slows down the correcting action of the actuator bullet or valve 16 of Figure 2 as the tailpipe temperature approaches the calibration temperature of the amplifier and minimizes control correction overshoot; its action is analogous to that of a dashpot in that it ac hievw control stability by reducing the controls correction speed without affecting the sensitivity or actuating forces of the control under stall conditions.

A speed switch and relay circuit is indicated at it includes an engine driven speed switch 86, which is shown in the form of a governor 86 adapted to separate a pair of spring-pressed contacts 87 and 88 when the engine speed attains a predetermined value. Also, in the circuit 85 is an arming relay K2, provided with an armature 89, which is connected to a switch 90. As shown, switch 90 is of the normally closed type, that is, it is urged into engagement with a contact 91 by a spring 92 when the relay coil is unenergized; and when said coil is energized, switch 90 is moved into engagement with a contact 9S. With switch 90 in engagement with contact 91 (engine speeds in excess of a predetermined value), the variable phase winding 71 of motor 39 is connected to the secondaries TSF and TSC of the magnetic amplifier TS. When switch 90 is in engagement with contact 9S (engine speeds below a predetermined value), the said variable phase winding 71 is connected to the volt supply. The manner in which these respective switch positions affect the operation of the system will be explained in the description of operation, which follows:

Operation It is assumed that the control is to be used with a fuel feed device having an all-speed governor-type fuel or throttle valve which will automatically maintain a steady engine speed for a given throttle or power lever setting. The curve chart of Figure 6 further assumes that the fuel head `across the throttle valve metering restriction is automatically regulated as a function of engine speed, as in the Mock application Serial No. 156,980, heretofore noted.

With reference to Figures l, 2 and 3, the power lever 18 is at a part-throttle setting (throttle position between 0 and 52), the throttle cam 52 of Figure 2 is in its ineffective range of movement with respect to follower rod 51, the bullet valve 16 is set for maximum jet area, and speed switch 86 is closed so that relay switch 90 is against contact 9S and the voltages supplied to the field windings 70 and 71 of the actuator motor 39 are in such a phase relationship as will hold the one end of the stop arm 42 against the overtemperature stop 44. Also, the cam S7 is holding the servo valve pistons 30 and S1 in their extreme left hand positions so that annular recesses S2 and SS are open and high pressure fluid or oil is being vented to that side (bottom side in yFigure 2 or right hand side in Figure l) of the actuator piston 25, which is effective to hold the bullet valve 16 in its maximum area position. This is the unarmed position of cam S7.

If now the pilot should move the power lever 18 from part-throttle to maximum power position (90 position) to accelerate from point A to G in Figure 6, the all-speed fuel governor spring (not shown) would be reset and the throttle valve would begin to open. With an exhaust jet area as at M (maximum opening), it requires only a relatively slight increase in the fuel feed rate to accelerate from A to a point beyond the surge area, since the drop across the turbine is at a maximum.

With the throttle or power lever 18 set at maximum power position, the speed switch 86 open, and engine temperature below a predetermined safe value, cam 37 rotates to the position shown in dottled lines in Figure 2 and arm 42 engages the under-temperature stop 4S. Throttle cam 52 will have been rotated clockwise and will, under these conditions, be effective to move servo valve pistons S0 and S1 to the right and vent high pressure fluid 'or oil to the area-reducing side (top side in Figure 2 or left hand side in Figure l) of the actuator piston 25 by way of port S5 and oil line 26. The bullet valve 16 will Vto the degree and rate 'and increase the exhaust jet area.

then move to the minimumarea or maximum thrust position at G. rl`his reduction in area of the exhaust jet decreases the drop across the turbine (back pressure rise), and were it not for the all-speed governor action on Ythe fuel valve, the engine would slow down. However, the governor now calls for a sharp increase in `fuel to maintain the speed selected by the setting of the power lever 18, and the acceleration fuel increase to approximately the maximum temperature limit, viz., a temperature which may be maintained only temporarily or just during acceleration, and follows the maximum temperature line to where governor cut-off begins, whereupon it decreases to steady-speed operating point G.

The pilot is at liberty to reset the throttle or power control lever from idle or low power to maximum power position (90 position) suddenly or in one motion without danger of bringing about an overtemperature condition. This is so, since in order for the bullet valve 16 to close (a) the speed switch 86 must be open, and (b) the turbine temperature must be below a predetermined safe value. As the throttle or power lever 18 moves through the 93 position, cam 52 acts through rod 51 and lever 48 to move cam 37 to the right, but if the speed switch is closed, cam 37 will remain in its full-line position and will have moved valve pistons 30 and 31 to the left a distance such that the cam 52 becomes ineffective to move said pistons sufficiently far to the right to open port 35 to high pressure oil or fluid. As long as the speed switch remains closed, the variable phase winding 71 is energized by 400 cycle supply voltage and the phase relationship between windings 70 and 71 is such as will cause the motor to rotate the contact end 42 of arm 42 `against the overtemperature stop 44 (solid line position of cam 37), at which point the motor stalls. When the speedl switch opens, the variable phase winding 71 is energized through the amplifier. If, for example, the engine temperature is at 1255 F., which will be presumed to be the maximumrcontinuous engine operating temperature, the motor torque is such as to just balance out the opposed force of spring 41 and the contact end 42 of arm 42 remains against stop 43, but if the temperature rises above 1255 F., the amplifier puts outa signal to' the variable phase winding which is proportional of temperature rise, and the motor 39 rotates cam 37 to some intermediate position, thereby moving servo valve pistons 30 and 31 to'the left and causing hydraulic motor piston4 25 to move upwardly As the area increases, two things happen simultaneously:V the follow-up mechanism, including worm 61 and shaft 62, starts to recenter the valve pistons 30 and 31 and the temperature drop reduces the voltage to the motor 39, causing the motor cam 37 to rotate such that it also starts to recenter the Valvevpistons. As long as theovertemperature condition exists, the nozzle area increases until an area is reached where the turbine temperature is 125 5 F. When this temperature is reached, ther amplifier output is reduced, the pilot valve pistons have centered, movement of power piston 25 has stopped, 'and the jet nozzle area arrived at is maintained.

` Resuming the description of operation in conjunction withV Figure 6, as the speed of the engine increases to the point indicated by the vertical line 94, speed switch 86 opens, the relay coil of K2, VFigure 3,` is de-energized and spring 92 moves switch 90 into engagement with contact 91. The amplifier now supplies voltages in such 'phase relationship to the field windings 70 and 71 of motor 39 as will cause the motor to rotate arm 42, -Figure 2, yagainst Vthe under-temperature stop 43. The actuator is now armed and the pilot has complete control of bullet valve position by moving lever 1S` within a range of say, 52 to 90, subject, however, to being overridden by the temperature responsive amplifier in the event of a rise in turbine or tailpipe temperature above a predetermined value with the bullet valve in aparassu-11e 10 tially closed position. This upper temperature limit is the calibration or set temperature of the amplifier, and should this be exceeded, the field windings of motor 39 will be supplied with voltages in such phase relationship as will cause the motor armature or shaft 42 to rotate clockwise, rotatingcam 37 in a direction to move servo valve pistons to the left and vent high pressure uid to the underside of actuator piston 25 and venting the opposite side thereof to drain. The exhaust jet area will then be increased until the turbine or tailpipe temperature equals the amplifier set temperature. A rise in turbine or tailpipe temperature (more briefly expressed as engine temperature) at a given setting of the pilots control lever may result from changes in altitude, ambient air temperature and other factors varying with cngines having different characteristics. When the bullet valve 16 reaches any one of its given positions, the followup cam 58 of Figure 2 will have centered or balanced the servo valve pistons 30 and 31, and power piston 25 will-then be held against further movement until the pilot valve pistons are again displaced through rotation or axial movement of cam 37;

Assume the engine is operating at a speed below that required to close switch 19 when the throttle is rotated into the after burner range position, which lies between 93 to 110. The afterburner control device 17" will be actuated via the linkage 21 but fuel cannot be fed to the afterburner manifold at this time because the normally closed solenoid valve 19 remains closed until energized by the closing of the switch 19". If the engine is operating at the speed setting of the switch 19 when rotation of the throttle 18 into the afterburner range, 93 to 110, occurs, the afterburner control device 17" is actuated as above noted, except that now the solenoid valve 19 `is open to allow additional fuel to be supplied to the engine Via the manifold 17".

Since the face 52 of the cam 52 has to will not effect movement of the follower rod 51. That is, where cam 52, of Figure 2, is used there will be no manual control of the exhaust area opening in the afterburner range of the engine; the servo valve 28 will be under the sole control of the electronic engine temperature sensing system at this time. However, with the use of cam 52", Figure 2a, the pilot continues to exercise control over the exhaust area opening in the afterburner range subject to further control by the electronic engine temperature sensing system.

Should the pilot decelerate as indicated by the dotted arrow line in Figure 6, cam 52 will be rotated counterclockwise back to the position shown in Figure 2 and the spring-pressed follower rod 51 will move to the left, causing servo valve 28 to move power piston 25 in a direction to retract the bullet valve 16.

Should there be an electrical power failure, the spring 41 will cause the end 42 of arm 42 to engages the under temperature stop 43 and move cam 37 to the dotted line position. This action will cause the pilot or servo valve pistons to move to the right such distance as will open the upper side of power piston 25 to pressure and the lower side to drain, and effect a reduction in exhaust jet area to a point where full engine thrust or power may be developed 'through operation of the pilots control lever, or by variation in the rate of fuel feed.

To summarize the operation:

(a) At engine speeds below speed switch setting, speed switch 86 is closed, switch 90 of relay K2 is against contact 92 and the motor 39 is energized by a fixed phase voltage and the 400 cycle supply voltage. This causes the motor to rotate stop arm 42 with the end 42 thereof against overtemperature stop 44. Motor cam 37 is then in the full line position, holding pilot valve 28 open so that pressure fluid is vented to the rod side of power pistion y25 and the bullet valve 16 fully retracted (maximum jet area). These conditions are maintained for power 11 lever positions from say zero to 52, although, as heretofore noted, during acceleration the power lever can be moved to full thrust position and the speed switch will still remain closed until the speed attains a predetermined value.

(b) At engine speeds above setting of switch 86 and power lever positions above 52, the said switch opens and the variable phase of motor 39 is energized through the amplifier of Figure 3. If engine temperature is at the upper limit, the motor produces sufficient torque to just balance out the force of spring 41, but not enough to move the end 42' to stop arm 42 away from underternperature stop 43. If engine temperature is below the upper limit (amplifier set temperature), the motor cam 37 turns to the dotted line position with the end 42 of arm 42 against undertemperature stop 43, throttle cam 52 has caused pilot valve 28 to open the hydraulic pressure line 26 to the upper side of power piston 25', and bullet valve 16 moves toward closed or minimum jet area position. As said valve 16 moves in its area decreasing direction, it acts through follow-up shaft 62, cam 58 and rod 50, to return pilot valve pistons 30 and 31 to centered position when the selected nozzle area is reached.

(c) Should the engine temperature exceed the set temperature (12.55 Fahrenheit), the amplier puts out a signal to the variable phase winding 71 of motor 39 which is approximately proportional to the combined error signal, correction rate signal, and temperature rate signal; whereupon said motor rotates cam 37 to some intermediate position, followed by movement of pilot valve pistons 30 `and 31 to the left and retraction of bullet valve i6. As bullet valve 16 retracts, follow-up cam S starts to recenter the servo valve pistons and the drop in temperature resulting from an increase in jet area reduces the voltage to motor 39, whereupon motor cam 37 is rotated in a direction such that it also starts to recenter the said servo valve pistons. As long as an overtemperature condition exists, jet nozzle area will increase until an area is reached where the engine temperature equals the amplifier set temperature. When this temperature is reached, pilot valve pistons 3? and 31 will have centered and further movement of power piston 25' is stopped.

Although only one embodiment of the invention has been illustrated and described, various changes in form and relative arrangement of parts may be made to suit requirements.

W e claim:

l. in a fuel feed and power control system for a turbojet engine having an exhaust jet, valve means for varying the effective area of the jet, a hydraulic actuator for said valve means, a servo valve for said actuator, fuel feed regulating means including a main fuel contro-l and an afterburner control, a power control member connected to said main and afterburner controls and movable between minimum and maximum power settings and between the latter land a maximum thrust augmentation setting, means operatively connecting said member to said servo valve in a manner such that over a range of movement of said member between a minimum power setting up to a given intermediate power setting the servo valve holds a position which causes the actuator to maintain the area of the jet substantially maximum, movement of said member from the intermediate setting to a substantially maximum power setting is effective through said last mentioned means to `adjust the servo valve to cause the actuator to move the valve means in a direction to reduce the area of the jct, and movement of said member from said maximum power setting to a thrust augmentation setting is effective through said last mentioned means to radjust the servo valve to cause the actuator to move the valve means in a direction to increase the area of the jet, said power control member being so arranged that move- .ment of said member between minimum and maximum power settings coordinates fuel flow from the main fuel control with jet area, movement of said member between maximum power setting and a maximum thrust augmentation setting coordinates fuel flow from the afterburner fuel control with jet area, an electric servo motor also operatively connected to said servo valve for adjusting the latter and arranged to override control of the servo valve by said member, an electric circuit for energizing said servo motor including a device for establishing a signal representing deviations in temperature from a given engine temperature, the circuit arrangement being such that at engine temperatures below said given value the servo motor is ineffective to override control of the servo valve by said member but at temperatures above said given value the servo motor overrides such control and becomes effective to adjust the servo valve in a direction to produce an increase in the area of the jet.

2. A fuel feed and power control system as claimed in claim l wherein said circuit is provided with means responsive to engine speeds below a predetermined value to cause said servo motor to adjust said control device to produce a minimum jet area, and means responsive to engine speed beyond said predetermined value for connecting the servo motor so that it responds to overtemperature signals.

3. In la fuel feed and power control system for a turbojet engine having an exhaust jet, valve means for varying the effective area of the jet, a power actuator for said valve means and an adjustable control device for said actuator, fuel feed regulating means including a main fuel control and an afterburner control, a power control member connected to said main and afterburner controls and movable between minimum and maximum power settings and between the latter and a maximum t-hrust augmentation setting, means operatively connecting said member to said control device in a manner such that over a range of movement of said member between a minimum power setting up to a given intermediate power setting the effective jet area is maintained substantially maximum, movement of said member from the intermediate setting to a substantially maximum power setting is effective to adjust said control device to cause the actuator to move said valve means in a direction to reduce the `area of the jet, and movement of said member from the maximum power setting to a thrust augmentation setting is effective to establish a predetermined jet area, said power control member being so arranged that movement of said member from minimum to maximum power setting is effective to operate said main fuel control, movement of said member from maximum power setting to a thrust augmentation setting is effective to operate said afterburner fuel control, an electric servo motor also operatively connected to said control -device for adjusting the latter to thereby override control by said member, an electric circuit for energizing said servo motor including a device for establishing a signal representing deviations in temperature from a given engine temperature, the circuit arrangement being such that at engine temperatures below said given value the servo motor is ineffective to override control by said member but at temperatures above said given value said servo motor overrides control by said member and becomes effective to adjust said control device in a direction to produce `an increase in the area of the jet whether the power control member is set for maximum power or thrust augmentation.

4. In a power control system for a turbojet engine having an exhaust jet and -an afterburner, valve means for varying the elfective area of the jet, a hydraulic actuator for said valve means, a servo valve for said actuator, ya fuel control device for said afterburner, a power control member movable between minimum and maximum power positions, means operatively connecting said member to said servo valve and said fuel control device such that over a range of movement of said 13 member between a minimum power setting up to a given higher power setting the servo valve positions the actuator to maintain a scheduled maximum jet area and from such given higher setting to la setting corresponding to maximum non-afterburning power setting said member becomes elect-ive to adjust the servo valve to cause the actuator to move the valve means `in a direction to reduce the area of the jet, and during the afterburner range of operation said member is connected to `control fuel flow to said afterburner as la function of the position of said member and to control said actuator such that the effective area of the jet is maintained at a minimum, an electric servo moto-r, means operatively connecting said servo motor to said servovalve for adjusting the latter including means Afor overriding control of the servo valve by said member, land electrical means for ener- 14 gizing said servo motor including a device for establishing -a signal representing deviations in engine temperature from a predetermined value wherein signals indicating engine temperatures below said predetermined value render said servo motor ineffective to overr-ide control of the servo Valve by said member and signals indicating temperatures -above such a value render a servo motor effective to override such control and adjust -t-he servo valve in a direction to produce an increase in the area of the jet, I`and means `for rendering said override means operate at engine speeds above a predetermined value.

Jacobson Apr. 19, 1955 Baker et al. Mar. 27, 1956 

